Method and apparatus for cryogenic liquid expansion

Abstract

A method and apparatus for work expanding a cryogenic liquid wherein the liquid is expanded in a manner to avoid a transient pressure drop below the flash point thus reducing the potential for cavitation and consequent operating inefficiencies.

I claim: 
     
       1. A method for expanding a cryogenic liquid with reduced cavitation comprising: (a) providing the cryogenic liquid into a turbine comprising a shaft, an impeller mounted on the shaft, and a plurality N of turbine blades mounted on the impeller, N being within the range of from 0.8 to 1.2 times 20 D 0 .25 where D is the outside diameter of the impeller in inches forming N flow channels between the blades;   (b) expanding the cryogenic liquid by passing it through the N flow channels between the said plurality of blades thus imparting pressure onto the blades and developing pressure difference across each blade so as to cause rotation of the impeller and shaft; and   (c) removing the cryogenic liquid the turbine at a pressure less than its pressure when it entered the turbine.   
     
     
       2. The method of claim 1 wherein the cryogenic liquid is liquid nitrogen. 
     
     
       3. The method of claim 1 wherein the cryogenic liquid is provided into the turbine at a pressure within the range of from 400 to 1600 psia. 
     
     
       4. The method of claim 1 wherein the cryogenic liquid is removed from the turbine at a pressure within the range of from 50 to 200 psia. 
     
     
       5. The method of claim 1 wherein the cryogenic liquid experiences a pressure drop when it exits the turbine. 
     
     
       6. The method of claim 1 wherein D is within the range of from one to seven inches. 
     
     
       7. The method of claim 1 wherein at least one of said turbine blades is a partial blade. 
     
     
       8. The method of claim 7 wherein the turbine blades are mounted on the impeller in alternating fashion so that every full length blade is followed by a partial blade. 
     
     
       9. The method of claim 7 wherein each partial blade has a length such that the trailing edge of each partial blade is within the range of from 40 to 60 percent of the radius of the impeller. 
     
     
       10. The method of claim 1 wherein each blade has a thickness within the range of from 0.015 to 0.030 times the radius of the impeller. 
     
     
       11. An expansion turbine for work expanding a cryogenic liquid with reduced cavitation comprising: a shaft, an impeller mounted on the shaft, and a plurality N of turbine blades mounted on the impeller, N being within the range of from 0.8 to 1.2 times 20 D 0 .25 where D is the outside diameter of the impeller in inches. 
     
     
       12. The turbine of claim 11 free of any diffuser means attached to its exit. 
     
     
       13. The turbine of claim 11 wherein D is within the range of from one to seven inches. 
     
     
       14. The turbine of claim 11 wherein at least one of said turbine blades is a partial blade. 
     
     
       15. The turbine of claim 14 wherein the turbine blades are mounted on the impeller in alternating fashion so that every full length blade is followed by a partial blade. 
     
     
       16. The turbine of claim 14 wherein each partial blade has a length such that the trailing edge of each partial blade is within the range of from 40 to 60 percent of the radius of the impeller. 
     
     
       17. The turbine of claim 11 wherein each blade has a thickness within the range of from 0.015 to 0.030 times the radius of the impeller.